1. Field of the Invention
The present invention relates to a signal detection apparatus and a signal detection method in a radio station in an environment where a plurality of radio stations that share the same frequency band exist.
2. Description of the Related Art
In current radio communications, in many cases, a dedicated frequency band is assigned for each of radio communication systems to avoid mutual interference. However, in order to effectively utilize limited frequencies in radio communications, a method is being considered for using the same frequency band in a plurality of communication systems in recent years. Recently, cognitive radio technology is drawing attention as a scheme where a plurality of radio systems coexist in the same frequency band. In the cognitive radio technology, radio environment is recognized, so as to perform communication by setting transmission parameters such as center frequency, signal bandwidth, beam pattern and the like based on the recognition result and a rule for spectrum sharing. In particular, in an environment where a plurality of radio systems share the same frequency band, each cognitive radio apparatus needs to recognize use status of radio resources before starting transmission as accurately as possible in order to enhance frequency use efficiency while avoiding interference to a primary system and avoiding interference between cognitive systems.
As signal recognition techniques, there are power detection, matched filter detection, feature detection and the link. As a representative example using power detection, CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) scheme is known. This technique is described in the non-patent document 1, for example. In the CSMA/CA scheme which is used in radio LAN systems represented by IEEE802.11 standard, the reception level is measured before transmitting data to determine whether to transmit data. The patent document 1 and the non-patent document 2 disclose techniques in which each radio station performs detection of presence of a signal by calculating feature amount of cyclostationarity of the signal, and performs transmission only when the signal is not detected, so as to avoid interference. Such feature detection is a technique for utilizing statistical characteristics of the signal, and is advantageous in that advance information such as bandwidth and frame format is unnecessary, and that synchronization of time and frequency is unnecessary.
By using these techniques, it becomes possible that a radio station detects presence of a signal being used in adjacent areas, and performs transmission when it is determined that interference does not occur even when the same frequency band is shared among different radio communication systems.